Devin is planning to build exercise pens for his three horses. Because of the space that he has available, he has decided to create three rectangles pens. Each pen has the same size and shape. He has been told the perimeter of each pen should be 440 feet. He decides to use 1200 feet of fencing because this all he can afford. Write a system of equations that model this situation. What dimensions should Devin have for each pen? How would your equations change if the total amount of fencing was 800 feet?